Rotary grinding mill



N. E. HASTRUP ROTARY GRINDING MILL Sept. 22, 1970 4 Sheets-Sheet 1 Filed June 19, 1967 -llll.lllllll llll|llallla INVENTOR w4a EP/A #Azsmug BY m s, 47

ATTORNEYS Sept. 22, 1970 N E. HASTRUP ROTARY GRINDING MILL 4 Sheets-Sheet Z Filed June 19, 1967 N. E. HASTRUP ROTARY GRINDING MILL 4 Sheets-Sheet 3 INVENTOR v/4.s Ek/A ,v/zszvw BYRILMWW ATTORNEYS Sept. 22, 1970 Filed June 19, 1967 IIEIN Sept. 22, 1970 N. E. HASTRUP ROTARY GRINDING MILL 4 Sheets-Sheet 4.

Filed June 19, 1967 FIG. l3

FIG. I5

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INVENTOR NIELS ERIK HASTRUP 782M ,l fil w ATTORNEYS United States Patent O 3,529,781 ROTARY GRINDING MILL Niels E. Hastrup, Copenhagen-Valby, Denmark, assignor to F. L. Smidth & C0., New York, N.Y., a corporation of Delaware Filed June 19, 1967, Ser. No. 647,152 Claims priority, application Great Britain, June 23, 1966, 28,084/ 66 Int. Cl. B02c 17/06, 17/18 US. Cl. 241-181 12 Claims ABSTRACT OF THE DISCLOSURE A grinding mill for grinding material with grinding media, i.e. grinding bodies having associated with a grinding chamber a discharge chamber which is provided with lifters for continuously returning the grinding media from the discharge chamber to the grinding chamber substantially at the same rate at which the bodies enter the discharge chamber.

BACKGROUND OF THE INVENTION It has been previously known to construct a grinding mill for grinding material by means of a charge of loose grinding bodies by dividing the interior of the mill into two or more grinding chambers separated by perforated partitions, commonly known as diaphragms. Normally, each chamber has a charge of grinding bodies. The particular size of the grinding bodies utilized depends upon the degree of fineness required in the ground product. The diaphragms serve essentially as screens in allowing only the ground material to pass from chamber to chamber, while retaining the grinding bodies within their respective chambers. At the exit of the last chamber of the mill, or at the exit of the mill having only one chamber, there is also usually positioned a similar diaphragm.

Certain disadvantages have been found associated with the operation of such a mill. As is well known, the size of the finely ground product is directly proportional to the size of the grinding bodies; therefore, when a very fine-grained product is required, the use of very small grinding bodies is necessary. In the aforementioned mill, it has not been possible to produce very fine particle size with the use of very small grinding bodies since it has been found that these small bodies tend to easily pass through the perforations in the diaphragm of the mill along with the ground material, thereby making the later separation of the ground material from the grinding bodies extremely diflicult. To eliminate this problem, it has been proposed to make the perforations in the diaphragms smaller than the size of the grinding bodies; however, such technique makes it difficult to maintain an adequate flow of ground material through the diaphragm, decreasing the output rate of the mill. Further, this technique could only temporarily provide adequate separation since, in time, the size of the grinding bodies will be so reduced by natural wear that the grinding bodies would either clog the perforations in the diaphragm or pass directly through the perforations along with the ground material.

Additionally, other attempts have been made to provide adequate separation of the ground material and the grinding media emanating from a grinding mill. For example, screens have been positioned outside the mill to provide the necessary separation, as Well as to aid in the return of the grinding media to the interior of the mill. Not only do these external screen arrangements fail to entirely eliminate the aforementioned blockage problem, but the complicated nature of such arrangements prohibits their use for common grinding processes, due to the increased construction cost factor.

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Still further, annularly protruding partitions, commonly known as dam rings, have been used to retain the grinding bodies within the grinding chamber, but this technique alone has not proved successful.

SUMMARY OF THE INVENTION This invention relates to a rotatable, generally cylindrical, grinding mill for grinding material with a grinding media and comprises a grinding chamber having a material inlet; a discharge chamber positioned immediately adjacent to and communicating with the grinding chamber, said discharge chamber having a discharge outlet; a partition separating these chambers; and means within the discharge chamber for continuously returning, through the partition, any grinding media, that is, grinding bodies, to the grinding chamber from the discharge chamber.

Preferred means for returning the grinding bodies to the grinding chamber consists of at least one tube running essentially spirally from the periphery of the discharge chamber to a point radially inwards of the imperforate annular part of the partition which separates the grinding chamber from the discharge chamber. There may advantageously be two such essentially spiral tubes with their mouths from one another.

Other means for returning the grinding bodies to the grinding chamber through the partition may be used. It is well known to provide lifters in a granding mill to lift the charge and cause it to cascade through a grinding chamber. In the invention such lifters may be mounted in the discharge chamber adjacent to the partition that separates the grinding chamber from the discharge chamber to return the grinding bodies. The partition carries a central aperture to provide communication between the two chambers. Grinding bodies, which are normally steel balls, have an inherent tendency to rebound from any surface they strike and it has been found that the grinding bodies falling off the rotating lifters thereby tend to pass through the central aperture in the partition. With the use either of essentially spiral tubes or of lifters other means may be provided for aiding the return of the grinding bodies to the grinding chamber, as hereinafter described.

While it might be possible, during the actual operation of this novel mill, that some grinding bodies will pass into the discharge chamber, along with the ground material, this novel arrangement provides for the continual return of the grinding bodies from the discharge chamber at substantially the same rate as they enter it. While it might be true that some of the grinding bodies may indeed be discharged with the ground material from the discharge chamber at the start of the operation, the grinding bodies will all be returned once the process is in regular operation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical central sectional view of the invention taken on line 1-1 of FIG. 2;

FIG. 2 is a sectional view taken along lines 22 of FIG. 1;

FIG. 3 is a sectional view taken along lines 33 of FIG. 1;

FIG. 4 is a partial vertical central sectional view of a first modification of the invention;

FIG. 5 is an end view partly in section taken along lines 5--5 of FIG. 4;

FIG. 6 is a partial vertical central sectional view of a second modification of the invention;

FIG. 7 is a sectional view taken along lines 66 of FIG. 6;

FIG. 8 is a partial vertical central sectional view of a third modification of the invention;

FIG. 9 is a sectional view taken along lines 99 of FIG. 8;

FIG. 10 is a partial vertical central sectional view of a fourth modification of the invention;

FIG. 11 is a partial vertical central sectional view of a fifth modification of the invention;

FIG. 12 is a vertical central view of a modification in the outlet end of another mill of the invention;

FIG. 13 is a section taken along the lines 13-13 of FIG. 12;

FIG. 14 is a section taken along the lines .1414 of FIG. 12, and

FIG. 15 is a section taken along the lines 1515 of FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the embodiment illustrated in FIGS. 1 to 3 of the drawings, the rotary grinding mill is generally indicated by 1 and comprises an outer casing 2 and end walls 3 and 4. The mill casing 2 is divided into preferably a grinding chamber 5, a discharge chamber .6 and a distributing chamber 7. The grinding chamber carries a material inlet 8 located in end wall 3. Arranged immediately adjacent the grinding chamber 5 is the discharge chamber 6. An annular ring partition 10, having a central aperture 11, separates the grinding chamber 5 from the discharge chamber 6. The distributing chamber 7 is arranged immediately adjacent to the discharge chamber 6 with a partition plate 12 separating the respective chambers. The other end of the distributing chamber 7 is closed by the end wall 4 of the mill 1. The end wall 4 has a material outlet 13 extending therethrough.

On the discharge chamber side of the annular ring partition a plurality of lifters 14 are mounted. These lifters 14 extend radially inwardly from the inner surface of the discharge chamber 6. The lifters 14 are adapted to lift the grinding bodies from the lower portion of the casing 2, where grinding bodies accumulate, to a point above the ground material in the discharge chamber 6 where, upon falling from the lifters 14, the grinding bodies tend to pass back through the aperture 11 in the annular ring partitions 10, due to the turbulence occurring within the discharge chamber 6.

It is to be understood that the lifters 14 need not exactly extend radially inwardly from the inner surface of the discharge chamber 6, but may project within the discharge chamber 6 at any suitable angle, as long as the lifters 14 function to lift the grinding bodies within the discharge chamber 6 and allow the bodies to fall within the immediate vicinity of the aperture 11 of the annular ring partition 10. Still further, the lifters 14 may even be arcuate in shape and still accomplish the above purpose.

The partition plate 12 carries a central discharge material opening 16 and a plurality of material discharge arcuate slots 17 are positioned peripherally about the central opening 16. Located outwardly of each respective slot 17, an arced deflector 18 is mounted on the plate 12 to extend into the discharge chamber 6. Each deflector 18 is arranged so that it is concave in the direction towards its respective slot 17.

The distributing chamber 7 carries a plurality of scoops 20 positioned between the partition plate 12 and the end wall '4. The scoops 20 are arcuate in shape and are arranged Within the distributing chamber in such a way that they are concave in the direction of the material outlet 13. These scoops 20 thereby easily distribute the ground material passing through the slots 17 in the partition plate 12 to the material outlet 13 in the end wall 4.

Communicating with the material outlet 13 there is mounted an elongated hollow discharge conduit 21 through which the ground material is passed for final use.

The mill casing 2 is suitably rotated on a rail 23 and roller assembly 24. Further, the conduit 21 is mounted with the bearing assembly 22 so that it may rotate along with the mill casing 2.

The operation of this grinding mill may be described as follows. A desired amount of unground material, along with grinding bodies, such as grinding balls, is introduced into the grinding chamber 5 through material inlet 8. The rotation of the grinding mill 5 is initiated by a suitable motor (not shown). The casing 2 is rotated in the direction indicated by the arrow A in FIGS. 2 and 3. The material, after being ground to a desired size, passes through aperture 11 in the annular ring partition 10 and spills into the discharge chamber .6. The annular partition 10 retains the great majority of the grinding bodies within the grinding chamber 5; however, due to the turbulence within the grinding chamber 5, some grinding bodies are carried through the aperture 11 in the annular ring partition, along with the ground material, and settle in the discharge chamber 6.

The ground material is discharged into the distributing chamber 7 from the discharge chamber 6 through the central discharge opening 16 and discharge slots -17 in the partition plate 12. The ground material is then distributed into the hollow discharge conduit 21 by the action of the scoops 20 in the distributing chamber 7.

As already indicated, the annular ring partition 10 retains a large majority of the grinding bodies within the grinding chamber 5. However, the grinding bodies passing into the discharge chamber 6 are returned to the grinding chamber 5 at substantially the same rate as they enter the discharge chamber 6 by the action of the lifters 14 which lift the grinding bodies and allow them to fall within the discharge chamber. Due to the turbulence occurring from the speed of rotation of the mill 1, and due to the rebounding action of the grinding bodies, the grinding bodies falling from the lifters 14- tend to pass through the aperture 11 in the partition 10.

To assist in causing the grinding bodies to pass back through the aperture 11, the deflectors 18 are mounted on the plate 12. These deflectors 18 divert any grinding bodies downwardly away from the central opening 16 and the slots 17 in the partition plate 12 so that the grinding bodies may more easily come into contact with the lifters 14.

Once the ground material passes through the opening 16 and the slots 17, it is distributed by the scoops 20 from the distributing chamber 7 into the hollow conduit 21.

The modification illustrated in FIGS. 4 and 5 is closely similar to that shown in FIGS. 1-3. However, in this modification, the central aperture 11 in the annular ring partition 10 is surrounded by a frusto-conical ring 25, the purpose of which is to restrict to some extent the passage of grinding bodies from the grinding chamber 5 to the discharge chamber 6.

In addition to the lifters 14, two other means are progideg for returning grinding bodies to the grinding cham- Firstly, the discharge chamber 6 is provided with a lining 26 which tapers towards the material outlet 13 in the end wall 4 of the mill 1. The lining 26 may be made of any suitable material but must be of a shape such that it forms a frusto-conical discharge chamber having a diameter decreasing in the direction of the end wall 4 of the mill 1. The lining not only causes the grinding bodies present in the discharge chamber 6 to move towards the annular ring partition 10, but also provides a discharge chamber 6 which may have a somewhat lower internal per pheral speed near the material outlet 13 than that tacthrdeved near the ring partition 10 when the mill is ro- Secondly, a circular deflector plate 27 is suspended vertically within the center of the discharge chamber 6 facing the aperture 11 of the ring partition 10. The de flector plate 27 is supported by supporting rods 28 which are anchored to the end wall 4 of the mill 1. The deflector plate 27 forms an annular passage for material between the discharge chamber lining 26 and the edge of the deflector plate 27.

In this embodiment, the hollow discharge condurt 21 is provided with a rotating screw 30 having a central opening 31. The screw is rotated in the direction of the discharge chamber 6 and, therefore, conveys any grinding bodies back into the discharge chamber 6 if some should, by chance, find their way into the hollow discharge conduit 21. Since the screw has a central opening, its rotation in the direction of the discharge chamber 6 does not prevent the movement of the ground material through the hollow conduit 21 since the ground material easily passes through the screw opening 31.

The mill shown in FIGS. 6 and 7 differs from that shown in FIGS. 4 and only in that the frusto-conical ring 25, positioned about the central aperture 11 of the annular ring partition 10, is replaced by a ring 32 of triangular cross-section, and in that the deflector plate 27 carries a frusto-conical extrusion 33 extending outwardly from the deflector plate 27 towards the aperture 11 in the annular ring partition Both ofthese features have been found to increase the tendency of the grinding bodies to return to the grinding chamber 6.

The mill shown in FIGS. 8 and 9 has three discharge chambers, 34, 35 and 36, positioned adjacent the grinding chamber 5. Each discharge chamber is separated by annular partitions 37, 38 and 39, all carrying frusto-conical rings 25 about their apertures 11, similar to those illustrated in FIG. 4.

In the distributing chamber 7, scoops 20 are arranged for lifting ground material and distributing it to a screw 40 which has a short shaft of substantial diameter. The screw 40 is rotated such that its threads 41 convey the ground material away from distributing chamber 7 and into the hollow conduit 21 which itself is devoid of any threads. The end of the screw 40, facing the annular partition 39, is frusto-conical in shape to facilitate the return of the grinding bodies from the discharge chamber 36 to discharge chamber 35.

The mill shown in FIG. 10 resembles that shown in FIGS. 8 and 9 very closely, except that the diameter of each aperture 11 in each annular partition increases successively in the direction of the screw 40.

FIG. 11 illustrates a grinding mill similar to that shown in FIG. 10. However, this grinding mill carries an annular lining 42 arranged about the internal periphery of the last discharge chamber 36. This lining 42 thereby provides the discharge chamber 36 with an internal diameter smaller than the internal diameter of the preceding discharge chambers 34 and 35. The reduced diameter enables the discharge chamber 36 to have an internal peripheral speed less than that obtainable in discharge chambers 34 and 35 when the mill is rotated; accordingly, the tendency of the grinding bodies to leave the discharge chamber through the arced slots 17 is reduced.

FIGS. 12-15 show another preferred means for returning the grinding bodies from the discharge chamber to the preceding grinding chamber. In this mill there is a darn ring 10 with a frusto-conical ring 25, the ground material and grinding bodies passing through the dam ring 10 into a discharge chamber 6 as before. In this discharge chamber there are two essentially spiral tubes 43 and 44, each having a mouth 45 lying at the periphery of the discharge chamber 6 and arranged to move through the mass of grinding bodies that at any instant is on the bottom of the discharge chamber. As the mill continues to rotate some of these grinding bodies pass through the mouth 45 of the tube and move along the tube until they reach its other end 46, which is curved as shown in FIG. 12, to enter the central opening in the dam ring. These grinding bodies are thus returned to the preceding grinding chamber. In the discharge chamber 6 shown in FIG. 12 there is also a plate 27, here shown as supported by rods 28 from the end wall of the mill. The ground material passes over a frusto-conical lining 26 through openings 17 in a dam ring 12 to be picked up by scoops 20 and delivered into discharge conduit 21.

Having thus described the invention with particular reference to the preferred forms thereof, it will be obvious to those skilled in the art to which this invention pertains, after understanding the invention, that various changes and modifications may be made therein without departing from the spirit and scope of the invention, as defined in the claims appended hereto.

I claim:

1. A rotatable grinding mill for grinding material with grinding media comprising a cylindrical grinding chamber having a material inlet, an aligned cylindrical discharge chamber positioned immediately adjacent thereto and having an axial discharge outlet for the overflow discharge of the ground product, a disc-like partition disposed normal to the axis of said cylindrical chambers between the said chambers and having a central circular aperture, the ground material including a small portion of the grinding media flowing through said aperture from the grinding chamber into the discharge chamber, and means within the discharge chamber for returning said grinding media through said aperture to the grinding chamber.

2. The grinding mill according to claim 1 wherein said means for returning grinding media to the grinding chamber comprises at least one tube running essentially spirally from the periphery of the discharge chamber to a point radially inward of the disc-like partition.

3. The grinding mill according to claim 2 having two essentially spiral tubes having their mouths located apart.

4. The grinding mill according to claim 1 wherein said discharge chamber is closed at the discharge end by a flat plate having said axial discharge outlet therein, said plate carrying deflectors mounted radially outward of said outlet and projecting into the discharge chamber.

5. The grinding mill according to claim 1 wherein said discharge chamber is closed at the discharge end by a flat plate having a plurality of discharge openings including a central opening and a plurality of arcuate slots arranged in spaced peripheral relationship about said central opening, and said plate having a deflector mounted radially outward of each slot.

'6. The grinding mill according to claim 5 wherein the shape of each deflector is concave in the direction of each respective slot.

7. The grinding mill according to claim 5 including a discharge conduit and a distributing chamber disposed adjacent the discharge chamber for routing the ground material emanating from the discharge chamber to the discharge conduit.

8. The grinding mill according to claim 1 wherein a deflector plate is suspended within the discharge chamber.

9. The grinding mill according to claim 8 wherein said deflector plate is circular and faces the central aperture in the disc-like partition.

10. The grinding mill according to claim 1 wherein the internal surface of the discharge chamber is frusto-conical having its internal diameter decreasing in the direction of the discharge outlet.

11. The grinding mill according to claim 10 in which a discharge conduit communicates with the discharge outlet having a central opening extending therethrough, and a screw is fixed to the surface of the discharge conduit for conveying grinding media back into the discharge chamber while allowing the ground material to pass through the screw opening.

12. The grinding mill according to claim 1 in which a plurality of discharge chambers are arranged adjacent one another in series, the first discharge chamber being positioned immediately adjacent the grinding chamber, and said discharge chambers being separated from 8 one another by disc-like partitions each having a central 1,368,739 2/1921 Lindhard 24160 X circular aperture. 1,649,813 11/1927 Dalgaard 24130 References Cited 3,298,618 1/1967 Talpey 24146.17 UNITED STATES PATENTS FOREIGN PATENTS 1,520,537 12/1924 DeMarkus 241-153 X 5 1,055,927 4/1959 Germany.

1,630,992 5/1927 Waterman 241153 X 1,712,082 5/ 1929 Koppers. LESTER M. SWINGLE, Primary Examiner 2,332,701 10/1943 Dowsett 241-170 X 2,885,155 5/1959 Frankert 241 153 KELLY Assstant Exammer 3,144,212 8/1964 Klovers 241153 X 

